This application claims the benefit of Korean Patent Application No. 2001-74157, filed Nov. 27, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a developing apparatus of an electric photographic printer, and more particularly, to a developing apparatus of an electric photographic printer capable of preventing a developing agent from being scattered in a developing area.
2. Description of the Related Art
An electric photographic printer is an apparatus to print an image by transferring an electrostatic latent image formed at a photosensitive medium to a printing medium after developing the electrostatic latent image to a visible image using a developing agent. In this case, the developing agent is normally a magnetic one-element developing agent or a nonmagnetic two-element developing agent.
The two-element developing agent includes toner and a carrier mixed at a predetermined rate. The carrier adheres as a brush shape to a surface of a developing roller by a magnetic force of the developing roller, and the toner adheres to the carrier by an electrostatic force.
FIG. 1 is a sectional view schematically showing a structure of a developing apparatus 10 of the electric photographic printer using the two-element developing agent.
Referring to FIG. 1, the developing apparatus 10 includes a developing roller 13, a developing agent mixing roller 17, a developing agent supplying roller 18, a magnetic bar 19 and a housing 11.
The developing roller 13 includes a developing sleeve 14 and a fixing magnet 15. The developing sleeve 14 is a hollow cylindrical shape and rotatably installed at the housing 11. The developing roller 13 transfers a developing agent 1 to a developing area A facing a photosensitive medium 20 disposed at opposite to the developing roller 13 with respect to the developing area A. The fixing magnet 15 is installed inside the developing sleeve 14 and is a cylindrical shape having a plurality of fragments. The fixing magnetic 15 has a magnetic pole N1 disposed to face the developing area A, and magnetic poles, S1, N2, N3, and S2 disposed in a counterclockwise in order from the magnetic pole N1 with respect to a center of the developing roller 13. Moreover, a developing blade 16 is disposed in a predetermined space at one upper side of the developing sleeve 14, thus a thickness of the developing agent attached to the developing sleeve 14 can be adjusted to be thinner by a predetermined degree.
The developing agent mixing roller 17 is installed at a rear of the developing sleeve 14. The developing agent mixing roller 17 mixes two elements, such as the toner and the carrier, and allows the developing agent 1 to be electrically charged to have an electrostatic force.
The developing agent supplying roller 18 is disposed at a rear portion of the developing agent mixing roller 17 and supplies the developing agent 1 to the developing agent mixing roller 17.
The housing 11 has the developing sleeve 14, the developing agent mixing roller 17, and the developing agent supplying roller 18. An area of the developing sleeve 11a faces the photosensitive medium 20 through an housing opening portion 11a of the housing 11.
The magnetic bar 19 is disposed at an outside of upper and lower ends of the hosing open portion 11a and adsorbs the developing agent 1 scattered at the developing area A.
An operation of the developing apparatus 10 having the above structure will be described hereinbelow.
The developing agent 1 in the housing 11 is supplied to the developing agent mixing roller 17 by the developing agent supplying roller 18, and thus the toner and the carrier are mixed. The mixed developing agent 1 adheres to the developing sleeve 14 by a magnetic force of the fixing magnet 15 installed inside the developing sleeve 14 and forms a magnetic brush shape. When the developing sleeve 14 is rotated, the developing agent 1 attached to a portion of the developing sleeve 14 passes through the developing agent blade 16 and becomes thinner to a predetermined thickness.
When the portion of the developing sleeve 14 rotates continuously and is disposed at the developing area A, the developing agent 1, which has become thinner, moves to the photosensitive medium 20 by an operation of an electrostatic force of the electrostatic latent image of the photosensitive medium 20.
At this time, when the developing agent 1 has little electrostatic force due to an insufficient electric charge, the developing agent 1 is scattered. Yet, the scattered developing agent 1 adheres to the magnetic bar 19 disposed at an outside portion of upper and lower ends of the hosing open portion 11a of the developing apparatus 10 and is prevented from being discharged to the outside portion of the developing apparatus 10.
However, in the developing apparatus 10 described so far, since the magnetic bar 19 is disposed at the outside portion of the housing open portion 11a, the developing agent leaking out to the outside portion of the housing 11 of the developing apparatus 10 is adsorbed to the magnetic bar 19. Therefore, a problem occurs that the developing agent 1 scattered at the developing area A cannot be completely prevented from leaking out to the outside portion of the housing 11.
The present invention has been made to overcome the above and other problems of the prior art. Accordingly, it is the object of the present invention to provide a developing apparatus of an electric photographic printer capable of effectively preventing a developing agent scattered in the developing area from leaking out to an outside portion of the developing apparatus by forming a magnetic force brush between a developing roller and a magnetic bar disposed on an inside portion of the housing.
Additional objects and advantageous of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to achieve the above and other objects, a developing apparatus of an electric photographic printer to supply a two-element developing agent to develop an electrostatic latent image formed on a photosensitive medium includes a housing, a developing agent supplying roller disposed at a lower part of the housing to transfer the developing agent, a developing agent mixing roller disposed at one side of the developing agent supplying roller to mix the developing agent so that two elements of the developing agent can be mixed equally, a developing sleeve rotatably disposed at one upper part of the developing agent mixing roller to transfer the mixed developing agent to a developing area facing the photosensitive medium by rotating in a counterclockwise direction, a fixing magnet disposed inside the developing sleeve to have magnetic poles N1, S1, N2, N3, and S2 arranged from the developing area in the counterclockwise direction with respect to a center of the developing roller to allow the developing agent attached to the developing sleeve to be transferred to the developing area, and a magnetic bar disposed inside the housing to face the magnetic pole S1 of the fixing magnet through the developing sleeve, to form a magnetic force brush preventing the developing agent from being scattered as the developing agent passes through the developing area.
It is possible that the fixing magnet has the magnetic pole N1 disposed to face the photosensitive medium, and a sectional rotation sleeve area of the magnetic pole S1 is almost equal to a total sectional rotation sleeve area of the magnetic poles S2, N3 and N2.
In addition, the magnetic bar includes a magnetic pole with a magnetic polarity, which is opposite to that of the magnetic pole S1 of the fixing magnet, and the magnetic pole of the magnetic bar is disposed to face the fixing magnet. The magnetic bar is a rubber magnet.
Furthermore, the magnetic bar has magnetic force adjustment plates disposed at front and rear ends of the magnetic bar, respectively, and an installation position of the magnetic bar is determined by using a magnetic force distribution by the fixing magnet.
These and other objects and advantageous of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a section view schematically showing a structure of a conventional developing apparatus of an electric photographic printer;
FIG. 2 is a section view schematically showing a structure of a developing apparatus of an electric photographic printer according to an embodiment of the present invention;
FIG. 3 is a view showing a status of a scattered developing agent when the magnetic bar is removed from the developing apparatus of FIG. 2; and
FIG. 4 is a partial section view showing a magnetic distribution of a fixing magnet and attached to the developing sleeve by a magnetic force brush of the magnetic bar of FIG. 2.